1. Field of the Invention
The present invention relates generally to building materials. The present invention is more particularly, though not exclusively, related to a materials used to finish interior and exterior walls, namely, a sealing tape for use in conjunction with joint compound to seal drywall panels together, as well as for corner bead for interior and exterior corners.
2. Discussion of Prior Art
In modern construction, both commercial and residential building techniques typically incorporate the use of interior wall boards. These boards are available in standard dimensions of 4×8, 4×10, 4×12, for example, and are intended to be mounted to standard wood or metal studs having separations of typically 16 or 24 inches for walls and ceilings. These wall boards are generally referred to as drywall, and also may be called gypsum board, wallboard, gyp-board, and Sheetrock (a registered trademark of United States Gypsum Company). Drywall consists of a core of plaster-like gypsum sandwiched between layers of heavy paper. The long edges of the drywall panels are tapered so that when panels are set adjacent to each other, the factory edges create a shallow recess. This recess is intended to facilitate the smooth sealing of the drywall panels together using joint compound (also referred to as “mud”) and tape. The end of a drywall panel (normally the four-foot length) is cut, not tapered, and it is much more difficult to conceal the butt end or the cut edge.
Over the years, the methods for sealing drywall panels have evolved from a simple paper tape, to sophisticated elastic adhesive strips. For example, the original paper tape used to seal drywall joints consisted of a thick paper tape that was coated on top and bottom with joint compound and placed over a seam. This was allowed to dry, and one or more additional coats of joint compound were applied over the now-dry tape to smooth the seam to match the drywall panels. A variety of devices were also used to increase the speed of applying the paper tape and joint compound. One device, often referred to as a “bazooka,” dispenses both the paper tape and the joint compound simultaneously to cover seams in one simple step. If a seam is being taped by hand, the seam receives a bed of mud, then tape is applied, then more coats of mud are applied.
While the paper drywall tape is generally effective, it can be difficult to handle due to the slippery nature of the joint compound used to hold it in place, and it is prone to shrinkage when drying. This can be particularly problematic in seam applications where a significant volume of joint compound is necessary, that is, for larger seam widths (up to 0.375 inch, for example), factory to butt seams, and patchwork. When attempting to avoid the shrinkage of a sealed joint and reduce drying time, it has been common practice to minimize the thickness of the coat of joint compound between the paper tape and the drywall panels, often called the “bedding” coat. However, if too little joint compound remained between the paper tape and the drywall panel following application of the tape, the tape would simply fall off or “bubble” in the areas of very thin joint compound once it had dried. Excessive shrinkage, difficult application, and extended drying times have made paper tape an unpopular choice amongst many drywall professionals.
Another alternative taping method included the use of a mesh tape, formed with a mesh pattern of fibrous material. This mesh tape often is coated on one side with a slight adhesive material to facilitate placement of the mesh tape on the drywall panel. Once in position, this mesh tape is covered with joint compound and allowed to dry. Due to the rough and perforated surface texture of the mesh tape, joints sealed with this tape are often prone to cracking or showing the mesh pattern in the dried joint compound. This method often requires multiple coats to achieve a smooth wall surface.
Another drawback of the mesh tape is the ability of the joint compound to pass completely through the mesh if too much pressure is applied by the taping knife during the application process. In these instances, the upper surface of the mesh tape has no joint compound covering and can be totally exposed. Eventually, the mesh tape can simply peel from the wall leaving a checkerboard pattern of joint compound on the wall. Also, hairline cracks which develop in a wall, at a seam, or at corners, can be visible through the mesh tape, which would otherwise be hidden from view by an opaque tape, such as the paper tape described above. Such small cracks are particularly prevalent near doors or windows, often occurring with the first resounding closure of such openings.
As an alternative to traditional paper and mesh tapes, U.S. Pat. No. 5,486,394, entitled “Self-Release Self-Adhesive Drywall Tape,” discloses a drywall tape having a web layer sandwiched between a top layer and a base layer, with an adhesive coating on the base layer. This adhesive layer facilitated placement of the tape over a seam without the need for joint compound to retain its position. Once in position, the seam between the drywall panels could be covering with joint compound to create a continuous flat wall panel surface.
While the initial installation of the tape described in the '394 patent may be much easier than traditional paper tape, it has a serious drawback. Specifically, the tape is only held in place on the wall seam with the adhesive, instead of with joint compound which exhibits a superior bond to the drywall panels. Thus, when the adhesive eventually weakens, the tape will delaminate from the drywall panels, likely crack through the overcoat of joint compound, and leave an unsightly joint. Further, because the joint is not sealed using a joint compound that has similar expansion characteristics of the drywall panels themselves, walls exposed to severe temperature and humidity variations will be prone to cracking.
As another alternative, U.S. Pat. No. 5,687,523, entitled “Drywall Tape,” discloses a tape formed with an array of perforations intended to allow the joint compound to pass through the tape to contact the drywall panels. These perforations may help the mud under the tape to dry faster, but they do not facilitate the attachment of the tape to the drywall panels because the mud is directly in contact with the panel, and any joint compound passing through the perforations merely contacts the drywall panel in the areas of the pinhole perforations, and does not wick between the tape and the drywall panel.
U.S. Pat. No. 5,820,958, entitled “Non-Cracking, Smooth, and Flat Patch for Wall Cracks,” discloses a tape formed of an elastic membrane having adhesive strips which facilitate the attachment to the wall panels. This tape is positioned over a crack or joint in a wall, and the adhesive strips are pressed into place on the wall. Once in position, joint compound is applied to the outer surface of the tape to create a smooth wall surface.
While very easy to install, the tape of the '958 patent can be prone to cracking. This is particularly so when used with joint compound, as the elastic nature of the tape results in a pliable wall surface, which is inconsistent with the rigid nature of dried joint compound. As a result, cracks sealed using this tape often will quickly form new cracks and result in mud delamination from the elastic membrane.
In light of the above, it would be advantageous to provide a joint sealing tape that cooperates with the drywall panels so as to adhere securely to the panels with a gypsum to gypsum bond and adhesion by suction, while exhibiting similar expansion properties as the drywall, thereby minimizing cracking of joints and seams. It would also be advantageous to provide a joint sealing tape that is stronger, easy to apply, permanent, easy to manufacture, and relatively cost effective.